1. Field of the Invention
Embodiments of the invention relate to processing tools for forming and processing films on substrates, such as with UV light. In particular, embodiments of the invention relate to controlling the gas flow profile within a processing chamber.
2. Description of the Related Art
Materials with low dielectric constants (low-k), such as silicon oxides (SiOx), silicon carbide (SiCx), and carbon doped silicon oxides (SiOCx), find extremely widespread use in the fabrication of semiconductor devices. Using low-k materials as the inter-metal and/or inter-layer dielectric between conductive interconnects reduces the delay in signal propagation due to capacitive effects. The lower the dielectric constant of the dielectric layer, the lower the capacitance of the dielectric and the lower the RC delay of the integrated circuit (IC).
Low k dielectric materials are conventionally defined as those materials that have a dielectric constant k lower than that of silicon dioxide—that is k<4. Typical methods of obtaining low-k materials include doping silicon dioxide with various functional groups containing carbon or fluorine. While fluorinated silicate glass (FSG) generally has k of 3.5-3.9, carbon-doping methods can further lower the k value to approximately 2.5. Current efforts are focused on developing low-k dielectric materials, often referred to as ultra low-k (ULK) dielectrics, with k values less than 2.5 for the most advanced technology needs.
One approach for forming silicon containing films on a semiconductor substrate is through the process of chemical vapor deposition (CVD) within a chamber. Organosilicon supplying materials are often utilized during CVD of the silicon containing films. As a result of the carbon present in such a silicon supplying material, carbon containing films can be formed on the chamber walls as well as on the substrate.
Additionally, ultra low-k (ULK) dielectric materials may be obtained by incorporating air voids within a low-k dielectric matrix, creating a porous dielectric material. Methods of fabricating porous dielectrics typically involve forming a “precursor film” containing two components: a porogen (typically an organic material such as a hydrocarbon) and a structure former or dielectric material (e.g., a silicon containing material). Once the precursor film is formed on the substrate, the porogen component can be removed, leaving a structurally intact porous dielectric matrix or oxide network.
Techniques for removing porogens from the precursor film include, for example, a thermal process in which the substrate is heated to a temperature sufficient for the breakdown and vaporization of the organic porogen. One known thermal process for removing porogens from the precursor film includes a UV curing process to aid in the post treatment of CVD silicon oxide films. For example, U.S. Pat. Nos. 6,566,278 and 6,614,181, both assigned to Applied Materials, Inc., describe use of UV light for post treatment of CVD carbon-doped silicon oxide films.
UV chambers and processes may have non-uniform gas flows through the chamber during the UV curing process to remove porogen. The non-uniform gas flow may result in uneven heating of the substrate during the curing process, resulting in a temperature gradient across the substrate and uneven processing. Additionally, the UV processing chamber can become coated with intact porogen, fragmented species of porogen, and other porogen residues, including coating of the windows that permit UV light to reach the substrate. Because of non-uniform flow, the window may also be preferentially coated towards one edge of the substrate versus the other edge. Additionally, the non-uniform build-up of porogen residue on the window may result in unevenly cured film across the substrate.
With time, the porogen residue can reduce the effectiveness of the subsequent UV porogen removal processes by reducing the effective UV intensity available to the substrate and building up at the colder components of the chamber. Furthermore, the build-up of excessive residues in the chamber can be a source of particulate defects on the substrate which is unsuitable for semiconductor processing. Accordingly, thermally unstable organic fragments of sacrificial materials (resulting from porogens used during CVD to increase porosity) need to be removed from the processing chamber. Increased cleaning times and corresponding reduced throughput is thus necessary to remove porogen residue.
Therefore, a need exists to increase efficiency, throughput, and improve cleaning processes of processing chambers in a production environment, such as a UV processing chamber for a UV porogen removal process. Therefore, there exists a need in the art for a UV chamber that can increase throughput, consume a minimum of energy, and be adapted for in situ cleaning processes of surfaces within the chamber itself.